1. Field of the Invention:
The present invention relates to an optical device. More particularly, it relates to a novel optical device which is well suited for application to the field of optical information transmission (especially, optical communication) wherein an optical signal to be transmitted depending upon the ON/OFF or intensity of light is modulated by controlling it by means of an external factor such as light, electric field, magnetic field, stress or current.
2. Description of the Related Art:
As optical modulation devices, there have heretofore been known an optical modulation device which utilizes the electrooptic effect of an LiNbO.sub.3 dielectric (ROD C. Alferness, IEEE Journal of Quantum Electronics, Vol. QE-17, No. 6, pages 946-957 (June, 1981)) and an optical modulation device of the type applying an electric field, which utilizes the Franz-Keldysh effect of GaAs (T. H. Wood et al; IEEE Journal of Quantum Electronics, Vol. QE-21, No. 2, pages 117-118 (February, 1985)).
Such prior-art optical modulation devices utilizing the electrooptic effect and the Franz-Keldysh effect require voltage application magnitudes which are as high as 10 V-50 V, and they are difficult of converting high-speed signals into optical signals. Moreover, they are incapable of optical modulation of very high speed which the present invention realizes.
There has also been proposed an optical gate device wherein light is turned ON or OFF with the light itself by utilizing the excitonic absorption of a quantum well structure (J. L. Jewell et al, Appl. Phys. Lett., Vol. 46 (10), (May, 1985) pages 918-920).
Even the optical device utilizing the excitonic absorption, however, exhibits as long a switching time as 5 nsec and cannot be used as an optical switching device of ultra-high speed.